This invention relates in general to storage phosphor based computed radiography and more particularly to a fixture for aligning an image quality test target with storage phosphors of different sizes.
Storage phosphor based computed radiography (CR) systems use a storage phosphor screen to record a latent radiographic image of an object, such as a body part. The latent radiographic image is read out by a CR reader to produce a digital radiographic image which can be processed, stored, displayed or printed on print media. The storage phosphor screen can be contained in a cassette for ease of handling and protection. The Kodak Computed Radiography system uses a storage phosphor screen mounted on a rigid plate which is removably attached to a cassette. The cassette is mounted to a CR reader which detaches the storage phosphor screen from the cassette and processes the detached storage phosphor. Other CR systems use a flexible storage phosphor screen mounted in a conventional radiographic film cassette. Different storage phosphor screens are used for different radiographic needs. The Kodak CR system uses three different sized storage phosphor screens and cassettes 35 cmxc3x9743 cm, 24 cmxc3x9730 cm, and 18 cmxc3x9724 cm.
The ability to obtain high quality measurements for the testing and calibration of computed radiography equipment and the associated radiation storage panels is critical to providing assurance that the imaging capabilities of the system are within specifications. The ability to do this quickly and accurately is also of great importance both in the equipment production environment and in clinical practice. A new test target has been devised, U.S. patent application Ser. No. 09/525,089, filed Mar. 14, 2000, inventors Wang et al. which consists of a copper plate into which has been cut a pattern of squares. The target and associated software are used in the calibration of reading devices and in the testing of the three sizes of cassettes. In order for the test system to work, the target must be centered on the cassette with a high degree of accuracy and when a number of cassettes are to be tested, the repeatability of the target alignment can be critical to obtaining useful results. Alignment to the largest cassette to be tested can be simplified by making the target to the same size as the outer dimensions of the largest cassette. Alignment to smaller sizes can be very difficult as the cassettes are not easily visible under the target.
According to the present invention, there is provided a solution to the problems discussed above.
According to a feature of the present invention, there is provided a storage phosphor based computed radiography system apparatus for aligning a test target with storage phosphor assemblies of different sizes comprising; a rectangular tray for selectively holding at least a first storage phosphor assembly having a first rectangular size and a second storage phosphor assembly having a second rectangular size smaller than said first rectangular size; said tray having first and second nested receptacles for selectively holding said first or said second storage phosphor assembly and wherein said first receptacle is sized to hold a test target of said first rectangular size in alignment with a held storage phosphor assembly.
The invention has the following advantages.
1. Rapid, precise and simple alignment of a test target with multiple sizes of storage phosphor cassettes is obtained in a storage phosphor based CR system.
2. A test target alignment tray is provided which also stores and protects the test target.
3. A test target alignment tray is provided which is easily and inexpensively fabricated through vacuum or thermo-forming of polymeric material.